A variety of therapies, such as neurostimulation or therapeutic agents, e.g., drugs, may be delivered to a patient to treat chronic or episodic pain. Examples of neurostimulation therapies used to treat pain are transcutaneous electrical nerve stimulation (TENS), percutaneous electrical nerve stimulation (PENS), peripheral nerve stimulation (PNS), spinal cord stimulation (SCS), deep brain stimulation (DBS), and cortical stimulation (CS). Examples of drugs used to treat pain are opioids, cannabinoids, local anesthetics, baclofen, adenosine and alpha-blockers.
PNS, SCS, DBS and CS are typically delivered by an implantable medical device (IMD). An IMD delivers electrical stimulation therapy via electrodes, which are typically coupled to the IMD by one or more leads. The number and positions of the leads and electrodes is largely dependent on the type or cause of the pain, and the type of neurostimulation delivered to treat the pain. In general, an IMD delivers neurostimulation therapy in the form of electrical pulses.
SCS involves stimulating the spinal cord at specifically targeted locations, typically via leads and electrodes that are either surgically implanted post laminectomy, or inserted percutaneously in the epidural space. Delivering stimulation to the appropriate location on the spinal cord causes paresthesia that overlays the pain region to reduce perception of pain. SCS can result in the patient experiencing paresthesia in a relatively large area, including more than one limb. In some cases, SCS may be effective for neuropathic pain, such as neuropathy or radiculopathy that involves a significant portion of one limb and more than one dermatome.
PNS is typically used to treat patients suffering from intractable pain associated with a single nerve. PNS places a group of electrodes in very close proximity to, e.g., in contact with, and approximately parallel to a major nerve in the subcutaneous tissue. PNS may also place a group of electrodes in very close proximity to a nerve that may be deeper in the limb. Placing electrodes in very close proximity to the nerve may ensure that only fibers within that nerve are activated at low amplitudes.
PNS electrodes may be located on percutaneous leads, but for stability and to prevent stimulation of other tissues proximate to the target peripheral nerve, PNS electrodes are generally located within insulative material that wraps around a nerve, e.g., cuff electrodes, or on one surface of a flat paddle of insulative material placed under a nerve. In any case, the electrodes for PNS are placed in close proximity to the nerve “upstream” from the source of damage or pain, e.g., closer to the spinal cord than the region of damage or pain. When electrodes are implanted upstream, the paresthesia resulting from PNS may extend to a broader area innervated by the target peripheral nerve. Examples of upper extremity nerves that may be treated with PNS include the ulnar nerve, median nerve, radial nerve, tibial nerve and common peroneal nerve.
DBS and CS can be used to treat neuropathic and nociceptive pain through delivery of stimulation to various structures of the brain. In some cases, DBS may treat pain through delivery of stimulation to gray matter within the midbrain, or the thalamus, via electrodes implanted in the brain. CS may treat pain through delivery of stimulation to the sensory and/or motor cortex via electrodes placed in or on the cortex.
Therapeutic agents that treat pain may be delivered by an implantable pump, external pump, transdermally, or orally. Typically, an implantable pump delivers one or more therapeutic agents to a target location via a catheter. The target location may be intrathecal or extradural.